Cassini’s last ride.

There might be a few tears shed, but only among certain groups of very well-educated people, who have been following Cassini’s career closely for lo, these many years. No doubt some will raise a glass, toasting a life that has been full and successful beyond anybody’s expectations. They will wait for Cassini’s last words before the faraway voice is silenced forever, its final moments literally enveloped in a mystery that will never be solved.

The end will come right about 6:55am CDT, ending a life that began on a launch pad nearly 20 years ago. Cassini is a space probe, and it has been orbiting the giant ringed planet Saturn since 2004. With its fuel reserves almost gone, the technicians controlling the probe from the Jet Propulsion Laboratory in California will steer Cassini into a long dive into the thick clouds of the planet. Will it burn up in Saturn’s atmosphere? Will it crash onto its surface? Is there even a surface there upon which it could crash? We don’t know, but we do know a lot more about Saturn than we did when the probe was launched in October 1997.

A joint project between NASA and the European and Italian space agencies, the Cassini probe will wind up costing about $3.26 billion, with us American taxpayers footing about 80% of the bill. As space missions go, that’s pretty cheap. It’s been estimated that a manned mission to Mars might run about 100 times that cost. If we were to replicate the Apollo program today, which took American astronauts to the moon and back nine times from 1968-72, it would cost about $200 billion. So Cassini’s relatively low cost, which included no danger whatsoever to humans because it was unmanned, has been a bargain.

Artist’s conception of the Cassini-Huygens probe in Saturn orbit.

The scientists estimate the craft will reach speeds up to 70,000mph at the end, nearly three times the speed it achieved to escape Earth’s gravity after its launch. In an atmosphere like Earth’s, it wouldn’t take long for that kind of velocity to cause the ship to burn to ashes, but it’s anybody’s guess as to what will happen when it penetrates Saturn’s. We know that Saturn’s upper atmosphere is about 96% hydrogen, and the pressure there is about twice what it is at sea level here. The temperature, though, is colder, a lot colder: from 100-160 degrees Kelvin, which is roughly about 200 degrees below zero Farenheit. We know there is ice in the atmosphere, too. So how could anything possibly burn at that temperature, which is even colder than Wisconsin’s worst winters? From Cassini’s final transmissions, which take about an hour to reach Earth even at the speed of light, we may find out.

The probe is not small, either. It is the second-largest interplanetary probe ever launched, 22 feet high and 13 feet wide, eclipsed in size only by a pair of Soviet probes sent to Mars, Phobos 1 and 2, launched in 1988 (and both of which failed). It is named after the Italian-French astronomer Giovanni Cassini, who discovered four of Saturn’s moons in 1671-72. Part of the probe was the Huygens lander, named after the 17th century Dutch astronomer Christiaan Huygens, who discovered the moon Titan. The lander parachuted to the surface of Titan in January 2005, becoming the first Earth probe to land on the moon of another planet. Together, Cassini-Huygens had 1,630 interconnected electronic components, 22,000 wire connections, and nearly nine miles of cabling, all powered by some 73 pounds of radioactive plutonium-238. The heat from the element’s decay was converted to electricity by three radioisotope thermoelectric generators. There was some risk involved in using plutonium as the power source; NASA estimated that if something had gone wrong after launch and Cassini had plunged back into our atmosphere, more than 80% of the people on the planet would have been exposed, causing some 5,000 additional cancer deaths. But they also estimated there was only one in a million chance of that happening, and Cassini beat those odds easily. It is considered very unlikely there are any life forms on Saturn that might be impacted by the radiation resulting from Cassini’s destruction, especially considering there is very little of the plutonium left to be dispersed.

Cassini used planetary bodies for gravity assists on the way to Saturn, flying by Venus twice in April 1998 and June 1999, whipping all the way out to the asteroid belt and then back toward Earth, coming within a quarter-million miles of our moon in August 1999. From there it was back out to the belt, where it flew by the asteroid 2685 Masursky in January 2000. (At a distance of a million miles away, Cassini’s pictures of Masursky weren’t much, but they were enough to determine that the asteroid is about 12 miles in diameter, large enough to cause cataclysmic damage if it ever hits us.) By December of that year it was near Jupiter, taking six months to fly by and transmitting some 26,000 images of the giant planet and its moons, along with its faint rings. On October 10, 2003, when it was between Jupiter and Saturn, Cassini conducted experiments using radio waves that confirmed Einstein’s theory of relativity.

Cassini’s photos of the moon showed it hadn’t changed much since the last human visit in 1972.

Flying by Jupiter, Cassini was able to give us close-up views of the giant planet’s intriguing, violent atmosphere.

Arrival at Saturn, and the show begins.

July 1, 2004, was the day Cassini arrived at Saturn and took up station, beginning a mission that would last more than 13 years. On Christmas Day that year, the Huygens lander separated from Cassini and headed for Titan. It didn’t land for another 22 days, finally drifting down through the methane atmosphere for two and a half hours under its parachute. The lander’s batteries were designed to last just about that long and were turned on only 15 minutes before entering the atmosphere. Once on the surface, Huygens was able to transmit data up to Cassini for several minutes before going dark forever. Presumably, it’s still there.

From the surface of Titan, Huygens transmitted a photo of an orange landscape littered with rocks. The temperature at the surface was measured at a rather chilly 290 degrees below zero F. There was no welcoming committee.

Cassini flew on, orbiting Saturn and visiting many of its moons, of which there are now more than 60. Cassini itself discovered seven of them. The most interesting moons appear to be Titan, which the Huygens lander visited, and Enceladus, which scientists now believe might very well contain underground oceans and perhaps microbial life forms. During its descent to Titan’s surface, Huygens photographed areas that appear to be riverbeds, leading to the conclusion that standing “water” formed by hydrocarbons is on or near the surface.

The New York Times published a series of 100 of Cassini’s most stunning photographs, and it’s well worth a few minutes of your time: Cassini’s view of Saturn.

The probe’s observations of Saturn have provided data that will keep scientists busy for years. It observed an enormous storm roaring across the planet’s northern hemisphere that lasted for months, and a permanent hurricane at the south pole that is 5,000 miles across with winds over 300mph.

As bad as the Hurricanes Harvey and Irma were here, they’re nothing compared to what Cassini saw on Saturn.

The legacy of Cassini.

When I was in 2nd grade, I remember my father bringing home a high school science book from the school in Seneca, Wis., where he was principal at the time. The section on the planets was fascinating. That was back around 1965, four years before the first manned landing on the moon. The first probe to impact the moon had just landed in ’64, and probes to Mars and other planets were still on the drawing board. All we had for images of the planets were taken through Earth-bound telescopes, and they were often fuzzy and indistinct. A few years later, I was able to observe Saturn myself through a small telescope from our home in Potosi, in southwest Wisconsin. When I attended college at UW-Platteville, I took astronomy as one of my two required science courses (geography was the other).

During my junior high years I read a paperback sci-fi book about Captain Future, an astronaut who traveled throughout the solar system, battling the forces of evil. There was a book devoted to his adventures on each planet, and every one was different. Venus was swamps, Mars an arid desert, Jupiter covered by massive jungles, and Saturn was a world of vast prairies. Written in the 1940s, the series was said to have taken place in the 1990s and beyond into the 21st century. It was through the Captain Future series, and similar early sci-fi works, that young kids like myself got our first inkling of what outer space might be like.

We know now, of course, that the moon and the planets of our solar system are nothing like those depicted in the Captain Future series, that there are no swamps or jungles or prairies out there. What we did find is perhaps even more fascinating, if a little on the lonely side; whereas each of the planets in the series sported indigenous life forms and were able to be colonized by Earthlings, we now are pretty sure that life, if it exists at all elsewhere in our solar system, is of the microbial nature.

But you never know. That’s why we keep going out there. The challenges of manned exploration of the planets have so far proven too daunting for us to meet, but I’m pretty sure that by the middle of this century we will have landed humans on Mars, although they might not be Americans. There’s an updated version of an old Cold War-era joke: The young boy asks his dad, “What will we find when we get to Mars, Dad?” And he says, “Chinese, son.”

Eventually, though, we will get there, and who knows for sure what we will find? Some would say it’s an enormous waste of money and other resources, all of which could be put to better use here on Earth to improve human lives and our planet itself, and there’s something to be said for that. But that’s always been the case. The governments and companies that sent the early explorers sailing fragile wooden ships across the vast oceans of our planet didn’t know for sure what was out there, or even if there was a “there.” But they went anyway, and what they discovered was far more dazzling, and profitable, than anything they had dreamed of. I have a feeling that will be the case when we finally set foot on Mars and perhaps the moons of Jupiter and Saturn.

It might be a century before humans follow the path of Cassini to Saturn and Huygens down to the surface of Titan, but what these dutiful, hard-working probes did was show us the way, revealing some of God’s most awesome creation. Their very existence is a credit to human ingenuity and our willingness to work together to explore the unknown. Imagine what we could accomplish if we did that all the time.

The mysteries of outer space are waiting for us. Cassini has helped show us the way.